But, in reality, in did feel good to see Iago get crushed. "Are there no stones in Heaven But what serve for thunder? Precious villain!" (V.ii.234-35) and then he ran at Iago with a sword. This was a really cathartic moment, until Iago kills Emilia, which isn't really all that sad. Although, she did have a pretty crappy life. Maybe she was glad it was over.
I guess I can't look at it logistiacally, Shakespeare wouldn't have let Emilia reveal the truth about the handkerchief when it was convenient, or else the play would have been really short and Iago probably would have been dead or thrown out on the streets.